This invention relates to a relay drive circuit for driving relays to turn on and off power supplied to loads from a power supply outputting a given voltage.
A conventional circuit for driving various loads 2 of an automobile uses relays. For example, as shown in FIG. 13, the circuit comprises a coil RC of a relay RL connected at one end to a voltage output terminal of an in-car battery 1 and grounded at the other end via an operation switch SW and one of relay contacts RS connected to the voltage output terminal of the in-car battery 1 and the other grounded via loads 2.
When the operation switch SW is turned on and a voltage equal to or more than an actuating voltage required for actuating the relay contacts RS is applied to the coil RC, the relay contacts RS are actuated and conducted. On the other hand, when the operation switch SW is turned off and the voltage applied to the coil RC becomes equal to or less than a release voltage, the relay contacts RS are released and restored to a non-conduction state.
In an automobile, circuit parts of relays, fuses, connectors, etc., are mounted on an electric junction box intensively. Since the circuit parts generate heat, it is necessary to design so as not to exceed the heat resistance temperatures of the parts and the electric junction box.
However, in recent years, as the number of relays has been increased with an increase in in-car electrical components and relays have been placed at a high density with miniaturization of the relays, the effect of heat generation of the relays, namely, coils becomes large and the heat generation needs to be suppressed.
Generally, the relay actuating voltage is about 7-8 V, the relay release voltage is about 2-3 V, and the power supply voltage of the in-car battery is 12 V. Thus, the relay generates unnecessary heat as much as the voltage difference between the battery power supply voltage and the relay actuating voltage.
Then, as shown in FIG. 14, a conventional circuit is known which comprises a resistor R connected to a coil RC of a relay RL in series for decreasing an applied voltage to the coil RC, thereby reducing the heating value of the relay RL.
A relay drive circuit is proposed in Japanese Patent Laid-Open No. Hei 8-55551 wherein a drive transistor for supplying an excitation current to a relay coil is operated in a region in which it is not completely turned on, thereby decreasing an applied voltage to the coil.
Although the conventional circuit shown in FIG. 14 decreases the heating value of the coil RC of the relay RL, the resistor R generates heat, thus it is difficult to sufficiently decrease the heating value of the whole circuit.
Also in the conventional relay drive circuit described in Japanese Patent Laid-Open No. Hei 8-5555, the reduction part of the coil application voltage is converted into heat by other circuit parts of transistors, etc., thus it is still difficult to sufficiently decrease the heating value of the whole circuit.
Furthermore, in the conventional relay drive circuit described in Japanese Patent Laid-Open No. Hei 8-55551, if the actuated relay contacts are restored to a release state for a reason such as vibration or impulse, the relay cannot again be placed in an actuation state unless an operation switch is once turned off, then on.
It is therefore an object of the invention to provide a relay drive circuit that can decrease the coil heating value efficiently and hold relays in an actuation state reliably.
According to the invention, there is provided a relay drive circuit for controlling an excitation current supplied to relay coils with relay contacts placed between a reference power supply outputting a given voltage higher than a relay actuating voltage and a plurality of loads, thereby actuating or releasing the relay contacts, the relay drive circuit comprising a low-voltage power supply outputting a voltage lower than the given voltage and higher than the relay actuating voltage for supplying the excitation current to each relay coil from the low-voltage power supply.
According to the above configuration, an excitation current is supplied to each relay coil from the low-voltage power supply outputting a voltage lower than the given voltage output from the reference power supply and higher than the relay actuating voltage, whereby the relay contacts can be reliably actuated and the heating value from the coils can be reduced as compared with supply of the excitation current from the reference power supply.
According to the invention, there is provided a relay drive circuit for controlling an excitation current supplied to relay coils with relay contacts placed between a reference power supply outputting a given voltage higher than a relay actuating voltage and a plurality of loads, thereby actuating or releasing the relay contacts, the relay drive circuit comprising a low-voltage power supply outputting a voltage lower than the given voltage and higher than a relay release voltage, time count means for counting the elapsed time since the actuation time of each relay, storage means for storing a preset time, and control means for supplying the excitation current from the reference power supply when each relay is actuated and supplying the excitation current from the reference power supply until the expiration of the preset time since the actuation time of each relay, then supplying the excitation current from the low-voltage power supply.
According to the configuration, when the relay contacts are actuated, the excitation current is supplied to the relay coil from the reference power supply outputting the given voltage, and the excitation current is supplied from the reference power supply until the expiration of the preset time since the actuation time of the relay contacts, then the excitation current is supplied from the low-voltage power supply outputting a voltage lower than the given voltage output from the reference power supply and higher than the relay release voltage, whereby the actuation state of the relay contacts is reliably maintained and the heating value from the coils is reduced as compared with continuous supply of the excitation current from the reference power supply.
The setup time is preset a little longer than the time taken until the relay contacts are actuated from the supply start time of the excitation current to the coil, whereby the relay contacts can be actuated reliably.
In the relay drive circuit as mentioned above, the low-voltage power supply outputs a voltage lower than the relay actuating voltage.
According to the configuration, the excitation current is supplied from the low-voltage power supply outputting a voltage lower than the relay actuating voltage, whereby the heating value from the coils is furthermore reduced.
According to the invention, there is provided a relay drive circuit for controlling an excitation current supplied to relay coils with relay contacts placed between a reference power supply outputting a given voltage higher than a relay actuating voltage and a plurality of loads, thereby actuating or releasing the relay contacts, the relay drive circuit comprising a low-voltage power supply outputting a voltage lower than the given voltage and higher than a relay release voltage, a reference voltage circuit for supplying an excitation current to each relay coil from the reference power supply, a low-voltage circuit for supplying an excitation current to each relay coil from the low-voltage power supply, and a stop control circuit for stopping the excitation current supply from the reference power supply after the expiration of a predetermined time since the actuation time of the relay contacts after supply of the excitation current from the reference power supply.
According to the configuration, after the expiration of the predetermined time since the actuation time of the relay contacts after supply of the excitation current to each coil from the reference power supply, the excitation current supply from the reference power supply is stopped, then the excitation current is supplied from the low-voltage power supply outputting a voltage lower than the given voltage output from the reference power supply and higher than the relay release voltage, whereby the actuation state of the relay contacts is reliably maintained and the heating value from the coils is reduced as compared with continuous supply of the excitation current from the reference power supply.
The predetermined time is preset a little longer than the time taken until the relay contacts are actuated from the supply start time of the excitation current to the coil, whereby the relay contacts can be actuated reliably.
In the relay drive circuit as mentioned above, the low-voltage power supply outputs a voltage lower than the relay actuating voltage.
According to the configuration, the excitation current is supplied from the low-voltage power supply outputting a voltage lower than the relay actuating voltage, whereby the heating value from the coils is furthermore reduced.
Further, in the relay drive circuit as mentioned above, the stop control circuit comprises a capacitor and is built in the reference voltage circuit for lowering the applied voltage according to a predetermined time constant after the excitation current supply by voltage application to the coil from the reference power supply.
According to the configuration, the stop control circuit comprises a capacitor and is built in the reference voltage circuit for lowering the applied voltage according to a predetermined time constant after the excitation current supply by voltage application to the coil from the reference power supply, whereby a voltage higher than the relay actuating voltage is applied to the coil as long as a predetermined time and the relay contacts are actuated reliably.
Furthermore, according to the invention, there is provided a relay drive circuit for controlling an excitation current supplied to relay coils with relay contacts placed between a reference power supply outputting a given voltage higher than a relay actuating voltage and a plurality of loads, thereby actuating or releasing the relay contacts, the relay drive circuit comprising a low-voltage power supply outputting a voltage lower than the given voltage and higher than a relay release voltage, a reference voltage circuit for periodically supplying an excitation current as long as a preset time to each relay coil from the reference power supply when a relay actuation instruction is given, and a low-voltage circuit for supplying an excitation current to each relay coil from the low-voltage power supply when a relay actuation instruction is given.
According to the configuration, when a relay actuation instruction is given, the excitation current is periodically supplied as long as the preset time to each relay coil from the reference power supply outputting the given voltage and the excitation current is supplied to each relay coil from the low-voltage power supply outputting a voltage higher than the relay release voltage, whereby when the excitation current is supplied from the reference power supply, the relay contacts can be actuated and while the excitation current is supplied from the low-voltage power supply, the relay contacts are held in the actuation state. Resultantly, the heating value from the coils is reduced as compared with continuous supply of the excitation current from the reference power supply. If the actuated relay contacts are released for a reason such as vibration or impulse, when another excitation current is supplied from the reference power supply, the relay contacts are restored to the actuation state.
The setup time is preset a little longer than the time taken until the relay contacts are actuated from the supply start time of the excitation current to the coil, whereby the relay contacts can be actuated reliably.
In the relay drive circuit as mentioned above, the reference voltage circuit comprises an oscillation circuit for outputting a pulse signal having a pulse width of the setup time on a given period and a voltage supply circuit for supplying the excitation current from the reference power supply only while the pulse signal is output when a relay actuation instruction is given.
According to the configuration, when a pulse signal of a pulse width equal to the setup time is output on a given period and a relay actuation instruction is given, the excitation current is supplied from the reference power supply only while the pulse signal is output, whereby the excitation current is supplied from the reference power supply to the coil as long as the setup time every given period.
In the relay drive circuit as mentioned above, the lowvoltage power supply outputs a voltage lower than the relay actuating voltage.
According to the configuration, the excitation current is supplied from the low-voltage power supply outputting a voltage lower than the relay actuating voltage, whereby the heating value from the coils is furthermore reduced.